Philosophers
Mortimer Adler Rogers Albritton Alexander of Aphrodisias Samuel Alexander William Alston Anaximander G.E.M.Anscombe Anselm Louise Antony Thomas Aquinas Aristotle David Armstrong Harald Atmanspacher Robert Audi Augustine J.L.Austin A.J.Ayer Alexander Bain Mark Balaguer Jeffrey Barrett William Barrett William Belsham Henri Bergson George Berkeley Isaiah Berlin Richard J. Bernstein Bernard Berofsky Robert Bishop Max Black Susanne Bobzien Emil du BoisReymond Hilary Bok Laurence BonJour George Boole Émile Boutroux Daniel Boyd F.H.Bradley C.D.Broad Michael Burke Lawrence Cahoone C.A.Campbell Joseph Keim Campbell Rudolf Carnap Carneades Nancy Cartwright Gregg Caruso Ernst Cassirer David Chalmers Roderick Chisholm Chrysippus Cicero Tom Clark Randolph Clarke Samuel Clarke Anthony Collins Antonella Corradini Diodorus Cronus Jonathan Dancy Donald Davidson Mario De Caro Democritus Daniel Dennett Jacques Derrida René Descartes Richard Double Fred Dretske John Dupré John Earman Laura Waddell Ekstrom Epictetus Epicurus Austin Farrer Herbert Feigl Arthur Fine John Martin Fischer Frederic Fitch Owen Flanagan Luciano Floridi Philippa Foot Alfred Fouilleé Harry Frankfurt Richard L. Franklin Bas van Fraassen Michael Frede Gottlob Frege Peter Geach Edmund Gettier Carl Ginet Alvin Goldman Gorgias Nicholas St. John Green H.Paul Grice Ian Hacking Ishtiyaque Haji Stuart Hampshire W.F.R.Hardie Sam Harris William Hasker R.M.Hare Georg W.F. Hegel Martin Heidegger Heraclitus R.E.Hobart Thomas Hobbes David Hodgson Shadsworth Hodgson Baron d'Holbach Ted Honderich Pamela Huby David Hume Ferenc Huoranszki Frank Jackson William James Lord Kames Robert Kane Immanuel Kant Tomis Kapitan Walter Kaufmann Jaegwon Kim William King Hilary Kornblith Christine Korsgaard Saul Kripke Thomas Kuhn Andrea Lavazza Christoph Lehner Keith Lehrer Gottfried Leibniz Jules Lequyer Leucippus Michael Levin Joseph Levine George Henry Lewes C.I.Lewis David Lewis Peter Lipton C. Lloyd Morgan John Locke Michael Lockwood Arthur O. Lovejoy E. Jonathan Lowe John R. Lucas Lucretius Alasdair MacIntyre Ruth Barcan Marcus Tim Maudlin James Martineau Nicholas Maxwell Storrs McCall Hugh McCann Colin McGinn Michael McKenna Brian McLaughlin John McTaggart Paul E. Meehl Uwe Meixner Alfred Mele Trenton Merricks John Stuart Mill Dickinson Miller G.E.Moore Thomas Nagel Otto Neurath Friedrich Nietzsche John Norton P.H.NowellSmith Robert Nozick William of Ockham Timothy O'Connor Parmenides David F. Pears Charles Sanders Peirce Derk Pereboom Steven Pinker U.T.Place Plato Karl Popper Porphyry Huw Price H.A.Prichard Protagoras Hilary Putnam Willard van Orman Quine Frank Ramsey Ayn Rand Michael Rea Thomas Reid Charles Renouvier Nicholas Rescher C.W.Rietdijk Richard Rorty Josiah Royce Bertrand Russell Paul Russell Gilbert Ryle JeanPaul Sartre Kenneth Sayre T.M.Scanlon Moritz Schlick John Duns Scotus Arthur Schopenhauer John Searle Wilfrid Sellars David Shiang Alan Sidelle Ted Sider Henry Sidgwick Walter SinnottArmstrong Peter Slezak J.J.C.Smart Saul Smilansky Michael Smith Baruch Spinoza L. Susan Stebbing Isabelle Stengers George F. Stout Galen Strawson Peter Strawson Eleonore Stump Francisco Suárez Richard Taylor Kevin Timpe Mark Twain Peter Unger Peter van Inwagen Manuel Vargas John Venn Kadri Vihvelin Voltaire G.H. von Wright David Foster Wallace R. Jay Wallace W.G.Ward Ted Warfield Roy Weatherford C.F. von Weizsäcker William Whewell Alfred North Whitehead David Widerker David Wiggins Bernard Williams Timothy Williamson Ludwig Wittgenstein Susan Wolf Scientists David Albert Michael Arbib Walter Baade Bernard Baars Jeffrey Bada Leslie Ballentine Marcello Barbieri Gregory Bateson Horace Barlow John S. Bell Mara Beller Charles Bennett Ludwig von Bertalanffy Susan Blackmore Margaret Boden David Bohm Niels Bohr Ludwig Boltzmann Emile Borel Max Born Satyendra Nath Bose Walther Bothe Jean Bricmont Hans Briegel Leon Brillouin Stephen Brush Henry Thomas Buckle S. H. Burbury Melvin Calvin Donald Campbell Sadi Carnot Anthony Cashmore Eric Chaisson Gregory Chaitin JeanPierre Changeux Rudolf Clausius Arthur Holly Compton John Conway Jerry Coyne John Cramer Francis Crick E. P. Culverwell Antonio Damasio Olivier Darrigol Charles Darwin Richard Dawkins Terrence Deacon Lüder Deecke Richard Dedekind Louis de Broglie Stanislas Dehaene Max Delbrück Abraham de Moivre Bernard d'Espagnat Paul Dirac Hans Driesch John Eccles Arthur Stanley Eddington Gerald Edelman Paul Ehrenfest Manfred Eigen Albert Einstein George F. R. Ellis Hugh Everett, III Franz Exner Richard Feynman R. A. Fisher David Foster Joseph Fourier Philipp Frank Steven Frautschi Edward Fredkin Benjamin GalOr Howard Gardner Lila Gatlin Michael Gazzaniga Nicholas GeorgescuRoegen GianCarlo Ghirardi J. Willard Gibbs James J. Gibson Nicolas Gisin Paul Glimcher Thomas Gold A. O. Gomes Brian Goodwin Joshua Greene Dirk ter Haar Jacques Hadamard Mark Hadley Patrick Haggard J. B. S. Haldane Stuart Hameroff Augustin Hamon Sam Harris Ralph Hartley Hyman Hartman Jeff Hawkins JohnDylan Haynes Donald Hebb Martin Heisenberg Werner Heisenberg John Herschel Basil Hiley Art Hobson Jesper Hoffmeyer Don Howard John H. Jackson William Stanley Jevons Roman Jakobson E. T. Jaynes Pascual Jordan Eric Kandel Ruth E. Kastner Stuart Kauffman Martin J. Klein William R. Klemm Christof Koch Simon Kochen Hans Kornhuber Stephen Kosslyn Daniel Koshland Ladislav Kovàč Leopold Kronecker Rolf Landauer Alfred Landé PierreSimon Laplace Karl Lashley David Layzer Joseph LeDoux Gerald Lettvin Gilbert Lewis Benjamin Libet David Lindley Seth Lloyd Werner Loewenstein Hendrik Lorentz Josef Loschmidt Alfred Lotka Ernst Mach Donald MacKay Henry Margenau Owen Maroney David Marr Humberto Maturana James Clerk Maxwell Ernst Mayr John McCarthy Warren McCulloch N. David Mermin George Miller Stanley Miller Ulrich Mohrhoff Jacques Monod Vernon Mountcastle Emmy Noether Donald Norman Alexander Oparin Abraham Pais Howard Pattee Wolfgang Pauli Massimo Pauri Wilder Penfield Roger Penrose Steven Pinker Colin Pittendrigh Walter Pitts Max Planck Susan Pockett Henri Poincaré Daniel Pollen Ilya Prigogine Hans Primas Zenon Pylyshyn Henry Quastler Adolphe Quételet Pasco Rakic Nicolas Rashevsky Lord Rayleigh Frederick Reif Jürgen Renn Giacomo Rizzolati A.A. Roback Emil Roduner Juan Roederer Jerome Rothstein David Ruelle David Rumelhart Robert Sapolsky Tilman Sauer Ferdinand de Saussure Jürgen Schmidhuber Erwin Schrödinger Aaron Schurger Sebastian Seung Thomas Sebeok Franco Selleri Claude Shannon Charles Sherrington Abner Shimony Herbert Simon Dean Keith Simonton Edmund Sinnott B. F. Skinner Lee Smolin Ray Solomonoff Roger Sperry John Stachel Henry Stapp Tom Stonier Antoine Suarez Leo Szilard Max Tegmark Teilhard de Chardin Libb Thims William Thomson (Kelvin) Richard Tolman Giulio Tononi Peter Tse Alan Turing C. S. Unnikrishnan Francisco Varela Vlatko Vedral Vladimir Vernadsky Mikhail Volkenstein Heinz von Foerster Richard von Mises John von Neumann Jakob von Uexküll C. H. Waddington John B. Watson Daniel Wegner Steven Weinberg Paul A. Weiss Herman Weyl John Wheeler Jeffrey Wicken Wilhelm Wien Norbert Wiener Eugene Wigner E. O. Wilson Günther Witzany Stephen Wolfram H. Dieter Zeh Semir Zeki Ernst Zermelo Wojciech Zurek Konrad Zuse Fritz Zwicky Presentations Biosemiotics Free Will Mental Causation James Symposium 
Werner Heisenberg
In 1925 Max Born, Werner Heisenberg, and Pascual Jordan, formulated their matrix mechanics version of "quantum mechanics" as a superior formulation of Niels Bohr's old "quantum theory." The matrix mechanics confirmed discrete states and "quantum jumps" of electrons between the energy levels, with emission or absorption of radiation. But they did not yet accept today's standard textbook view that the radiation is also discrete and in the form of Albert Einstein's spatially localized "light quanta," which were about to be renamed "photons" by American chemist Gilbert Lewis in late 1926.
In early 1926, Erwin Schrödinger developed "wave mechanics" as an alternative formulation of quantum mechanics. Schrödinger disliked the idea of discontinuous quantum jumps of discrete particles. His wave mechanics is a continuous theory, but it predicts the same energy levels and is otherwise identical to the discrete theory in its predictions. Indeed, Schrödinger proved that matrix mechanics and his wave mechanics are isomorphic theories, but that quantum mechanical calculations are much easier to do using his wave mechanics. [The author used Schrödinger's wave functions to calculate the continuous spectrum of the hydrogen quasimolecule in his 1968 Ph.D. thesis at Harvard]
Within months of the new wave mechanics, Max Born showed that while Schrödinger's wave function evolves over time deterministically, it only predicts the positions and velocities of atomic particles statistically. Born applied to matter Einstein's view that the waves of radiation can be interpreted as probabilities for finding a light quantum. Einstein's view that the waves are "guiding fields" for the light quanta was described as public knowledge as early as 1921 by H. A. Lorentz and Louis de Broglie.
Even Heisenberg himself ultimately used Schrödinger's wave functions to calculate the "transition probabilities" for electrons to jump from one energy level to another. Schrödinger's wave mechanics is easier to visualize and much easier to calculate than Heisenberg's own matrix mechanics. Ironically, Schrödinger himself never accepted the existence of particles, neither matter nor energy, and hated the discrete "quantum jumps," preferring his continuous waves as explaining all quantum phenomena. These major disagreements between the founders of quantum mechanics continue to this day with diverse and conflicting "interpretations" of quantum mechanics, at most one of which can be correct.
In early 1927, Heisenberg announced his indeterminacy principle limiting our knowledge of the simultaneous position and velocity of atomic particles, and declared that the new quantum theory disproved causality. "We cannot  and here is where the causal law breaks down  explain why a particular atom will decay at one moment and not the next, or what causes it to emit an electron in this direction rather than that." Albert Einstein had shown this element of chance in his 1917 paper on the emission and absorption of light by matter, though Heisenberg did not explictly reference Einstein's work.
More popularly known as the Uncertainty Principle in quantum mechanics, it states that the exact position and momentum of an atomic particle can only be known within certain (sic) limits. The product of the position error Δx and the momentum error Δp is greater than or equal to Planck's constant h divided by 2π.
ΔpΔx ≥ ℏ = h/2π (1)
Indeterminacy (Unbestimmtheit) was Heisenberg's original name for his principle. It is a better name than the more popular uncertainty, which connotes lack of knowledge. The Heisenberg principle is an epistemological lack of information. But it does not claim that the ontological precise position and momentum do not exist, only that we can not know them, or, as Niels Bohr put it, that we cannot say anything about them.
Causality
Heisenberg was convinced that quantum mechanics had put an end to classical ideas of causality and strict determinism.
In his classic paper introducing the principle of indeterminacy, he concluded with remarks about causality. If one assumes that the interpretation of quantum mechanics is already correct in its essential points, it may be permissible to outline briefly its consequences of principle. We have not assumed that quantum theory — in opposition to classical theory — is an essentially statistical theory in the sense that only statistical conclusions can be drawn from precise initial data. The wellknown experiments of Geiger and Bothe, for example, speak directly against such an assumption. Rather, in all cases in which relations exist in classical theory between quantities which are really all exactly measurable, the corresponding exact relations also hold in quantum theory (laws of conservation of momentum and energy).But Heisenberg was not convinced that the lack of causality helped with the problem of human freedom. He reportedly said, "We no longer have any sympathy today for the concept of 'free will'." On the other hand, his close colleague, Carl von Weizsäcker, said that Heisenberg thought about the problem of free will "all the time." ( )
On Possibilities and Actuality
In his 195556 Gifford Lectures Physics and Philosophy Heisenberg described a quantum mechanical probability wave as a new version of the concept of "potentia" in Aristotle's Metaphysics.
He wrote, [The] probability function follows the laws of quantum theory, and its change in the course of time, which is continuous, can be calculated from the initial conditions...The probability function combines objective and subjective elements. It contains statements about possibilities or better tendencies ("potentia” in Aristotelian philosophy), and these statements are completely objective, they do not depend on any observer; and it contains statements about our knowledge of the system, which of course are subjective in so far as they may be different for different observers. Heisenberg also refers to Aristotle's ideas on pages 121123 and 134. "Matter is in itself not a reality but only a possibility, a "potentia"; it exists only by means of form." Unformed matter is an abstract concept. Particulate matter that "exists" has an intrinsic form, or an information structure, even if physicists have not measured it or observed it. Matter in thermal equilibrium, with maximum entropy, is said to lack information. In principle, that information exists objectively, even if we lack the subjective knowledge of it.
On Einstein's Light Quanta
Heisenberg must have known that Einstein had introduced probability and causality into physics in his 1916 work on the emission and absorption of light quanta, with his explanation of transition probabilities and discovery of stimulated emission.
But Heisenberg gives little credit to Einstein. In his letters to Einstein, he acknowledges that Einstein's work is relevant to indeterminacy, but does not follow through on exactly how it is relevant. And as late as the Spring of 1926, perhaps following Niels Bohr, he is not convinced of the reality of light quanta. "Whether or not I should believe in light quanta, I cannot say at this stage," he says. After Heisenberg's talk on matrix mechanics at the University of Berlin, Einstein invited him to take a walk and discuss some basic questions: I apparently managed to arouse Einstein's interest/for he invited me to walk home with him so that we might discuss the new ideas at greater length. On the way, he asked about my studies and previous research. As soon as we were indoors, he opened the conversation with a question that bore on the philosophical background of my recent work. "What you have told us sounds extremely strange. You assume the existence of electrons inside the atom, and you are probably quite right to do so. But you refuse to consider their orbits, even though we can observe electron tracks in a cloud chamber. I should very much like to hear more about your reasons for making such strange assumptions."
Heisenberg's Uncertainty Principle
What is the fundamental reason for our inability to measure position and momentum of a particle with arbitrary precision?
Heisenberg's Microscope claims that observations "disturb" a particle's position and momentum. The higher the energy of the observing radiation (the shorter the wavelength λ), in principle the microscope has increased resolving power, allowing the particle's position to be seen more clearly. But the higher energy means that the disturbance is more severe. Max Born, Heisenberg's colleague (with Pascual Jordan) in the development of matrix mechanics, said that the resolving power of a microscope is limited simply by its aperture and the wavelength λ of the observing radiation. Born described Heisenberg's failure to pass his thesis qualifying exam in experimental physics. Heisenberg could not answer Willy Wien's qualifying exam question on the resolving power of a microscope. It was only his top grade in theoretical physics that allowed Heisenberg to get his thesis approved. Niels Bohr, Heisenberg's mentor in Copenhagen and codeveloper of the Copenhagen Interpretation of quantum mechanics, showed uncertainty is not caused by a disturbance (which in principle can be accounted for). In 1927, at the Como conference, Bohr derived the uncertainty principle from the size of the minimum wave packet that can be formed from a combination of waves of different frequencies ν or wave numbers k. Heisenberg  A consequence of noncommutation of momentum p and position q operators, pqqp ≥ h/2πi. Boltzmann's phasespace volumes realized as h^{3} minimal quantum volumes?
Works
Talk with Einstein (1926)
BohrSchrödinger Meeting (1926) (PDF) Uncertainty Principle (1927) (PDF in German) Uncertainty Principle (1927) (PDF in English) History of Quantum Theory (PDF) The Copenhagen Interpretation of Quantum Theory (1955, Annotated) < The Copenhagen Interpretation of Quantum Theory (1955) (PDF)
For Teachers
For Scholars
